1. Field of the Invention
The present invention generally relates to a method of measuring a size. In particular, the present invention is directed to a method of indirectly measuring a size through a dimension independent of the size to be measured without destroying the sample. The method of the present invention is particularly suitable for measuring a sample with an extremely small size.
2. Description of the Prior Art
In the field of manufacturing a semiconductor element, it is often necessary to measure the size of the structural dimensions of products or semi-finished products in the manufacturing process. With the shrinkage the critical dimension of the semiconductor elements, for example less than 10 nm, it is a growing challenge to measure the very small size of the structural dimensions of products or semi-finished products. Meanwhile, the samples with the size to be measured also become smaller and smaller as the critical dimension of the semiconductor elements becomes smaller so the samples are more difficult to fabricate. There are some known methods to measure the size of a sample.
For example, for transmission electron microscopy (TEM), the first method involves a scanning electron microscope (SEM) but this method has numerous disadvantages. First, this method requires a scanning electron microscope. Second, this method requires a sample to be removed from one apparatus (in this example, a transmission electron microscope) to another apparatus (in this example, a scanning electron microscope), which takes too much waiting time. Moreover, each transfer of a sample will increase the risk of damage. Further, in order to manufacture a suitable sample for use in a scanning electron microscope, part of the sample is destroyed, which is not suitable for later inspection.
The second method is called a convergent electron beam diffraction (CBED) method. However, the disadvantage of this method resides in the use of non-traditional or advanced transmission electron microscopy analysis techniques, usually involving special software to analyze the data, and is not suitable for the sample thickness which is not thick enough, for example, it is not suitable for the measurement of a sample with a sample size less than 45 nm.
The third method is called an energy filter type transmission electron microscopy (EFTEM) method. But the problem is that, the result obtained in this method is the ratio of “thickness to size” t/λ (λ is the mean free path of the sample), rather than the thickness value per se. Additional hardware accessories are also needed in addition to a standard transmission electron microscope (TEM), and an advanced one is used in conjunction with transmission electron microscope operating techniques, which not suitable for general occasions.
In the light of the aforementioned commonly used methods, they cannot provide a method which is a simple, fast and direct operation. Therefore, a novel method is still need to simplify the measurement of a sample size.